Which statement is true about the inflow valve in the pressurization system?

• A. It is not a principal controlling component
• B. It is a primary control component
• C. It regulates cabin oxygen flow
• D. It measures cabin pressure

Answer: (A)

In a pressurization system, cabin pressure is controlled by a primary loop that governs how much air leaves the cabin. The inflow valve isn’t part of that regulating loop. Its job is to provide ambient air for ventilation and conditioning, not to set or maintain cabin pressure. The actual pressure control is accomplished by the outflow valve, which is adjusted by the cabin pressure controller to maintain the desired cabin altitude. The inflow valve doesn’t sense cabin pressure, doesn’t regulate oxygen flow, and doesn’t determine the pressure by itself, so it isn’t a principal controlling component. That’s why the statement describing it as not a principal controlling component is the correct one.